The early and late proteins of polyoma virus will be probed by in vitro mutagenesis. Subgenomic fragments of the viral DNA are cloned into single-stranded bacteria-phage M13 vectors, and mutagenesis is carried out using synthetic oligonucleotides as primers. A long germ goal is to understand structure-function relationships of the middle T protein, particularly in regard to its recognition by cellular protein kinases and to how phosphorylation events involving the middle T lead to cell transformation. Another long term goal is to understand the natural role of polyoma's transforming gene in the virus growth cycle. This will involve studies of the apparent requirement for phosphorylation of VP1, the major capsid protein, in the process of virus assembly. Sites of phosphorylation in middle T and VP1 will be identified and mutated, and the mutants characterized biologically and biochemically.